This invention relates to an injection molding machine and is particularly concerned with a coupling device associated with an automatically exchangeable working unit (formed of an injection mold assembly and a plasticizing unit) which may be moved away from the machine in a direction transverse to the axis of the injection. The coupling device serves to axially connect a periodically moved component of the working unit with an associated hydraulic driving device aligned with the axis of injection. The coupling device is of the type which has slidable locking bolts arranged diametrically relative to the axis of the injection and which, for effecting a coupling, may be moved by springs into an annular groove of one of the coupling components and are radially guided in a locking bolt housing which is affixed to the other coupling part. The coupling device further has a radially guided expander wedge which, for withdrawing the locking bolts from the annular groove, may be driven to a slight extent into a linear clearance between the locking bolts by means of a radially oriented piston-and-cylinder unit.
In an injection molding machine equipped in the above manner the injection molding unit may be attached to and withdrawn from the injection mold assembly accommodated in a mold closing unit, by means of at least one hydraulic power cylinder.
A known coupling device of the above-outlined type, as disclosed in German Patent No. 3,151,859, to which corresponds U.S. application Ser. No. 338,885, filed Jan. 12th, 1982, now abandoned, serves for effecting a releasable connection of the injection mold assembly (working unit) with its hydraulic drive. The separability of the drive from the working unit is an essential precondition for performing a centrally controlled exchange of the injection mold assembly (working unit) by means of a computer of the injection molding machine, wherein the working unit is removed or introduced in a direction transverse to the axis of injection. In order to be able to perform such a transverse conveyance, it is required to withdraw the coupling part provided with the annular groove from the locking bolt housing of the other coupling part in an axial direction thus rendering it free for transverse conveyance. This is achieved in the prior art construction by an axial stroke of the drive mechanism which is aligned with the axis of injection and which has to be designed to perform a correspondingly longer (relatively large) stroke. Since the sliding bolts work as radially locking members, very large torque loads may be taken up without the risks of damage.
German Offenlegungsschrift (Non-examined Published patent application) No. 3,229,223 discloses a coupling device which serves for connecting the feed screw rotating in the plasticizing cylinder and being capable of axial displacement, with a spindle which delivers a torque and also an axial shifting force. In this coupling device too, the axial stroke permitting a subsequent transverse conveyance is performed with the aid of a drive aligned with the axis of injection. The torque of the spindle is transmitted to the shaft of the feed screw by means of an overrunning clutch. Axial loads are taken up by an axial coupling which is constructed in a radially symmetrical manner, in alignment with the axis of injection and which is actuated by a separate, coaxial hydraulic drive cylinder that rotates with the coupling device. The supply of the hydraulic fluid thus involves additional structure and expense.